Synthesis of a delta opioid agonist in [2H6], [ 2H4], [11C], and [14C] labeled forms

Article abstract of DOI:10.1002/jlcr.1939

In support of a program to develop a treatment for depression, four labeled forms of a delta opioid agonist were prepared. The [²H₄] labeled form was prepared using a relatively straightforward conversion of [²H₄

Full text of DOI:10.1002/jlcr.1939

Research Article
Received 9 August 2011,
Revised 2 September 2011,
Accepted 12 September 2011
Published online 18 October 2011 in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/jlcr.1939
Synthesis of a delta opioid agonist in [2H6],
[2H4], [11C], and [14C] labeled forms
a
b
d,e
Charles S. Elmore, Kelly Brush, Magnus Schou, William Palmer,b
Peter N. Dorff,b Mark E. Powell,b Valerie Hoesch,b James E. Hall,b
Thomas Hudzik,c,f Christer Halldin,e and Cathy L. Dantzmanb
*
In support of a program to develop a treatment for depression, four labeled forms of a delta opioid agonist were prepared.
The [2H4] labeled form was prepared using a relatively straightforward conversion of [2H4]bromoethanol to [2H4]N-methyl-2-
hydroxyethylamine. The key step in the synthesis of the [2H6] labeled form involved the Pd-catalyzed exchange in D2O of 8-
quinolin-8-ol to give [2H6] 8-quinolin-8-ol. The C-14 labeled form was synthesized in one step using [14C]carbonylation, and
the C-11 labeled form was prepared in two steps from 11CH3I.
Keywords: [2H6]quinolin-8-ol; [2H4]ethanolamine; [14C]carbonylation; [11C]methylation
opted to utilize [2H4]-2-bromoethanol as the source of the
Introduction
labeled material (Scheme 3). Certainly, [13C, 2H3]methyl iodide
There are three distinct opioid receptor subtypes: mu, kappa, and
could have been used to good effect to achieve an enrichment
of M + 4 as well. The coupling of [2H4]-2-bromoethanol with
delta. Although these G-protein coupled receptors have a rela-
tively high sequence homology, they differ considerably in terms
methylbenzylamine proceeded in high yield to give
[ethyl-2H4]-3 as a clear oil. Using BnNH2 as the nucleophile pro-
of their pharmacology and distribution both in the brain and in
the periphery. All three receptors mediate analgesia but in a qua-
vided a product that could easily be detected by using spectro-
litatively different manner. For example, the effects of morphine
scopic means and that had enough mass such that the
are mediated by the mu opioid receptor, and typical mu opioid
compound was not easily lost because of volatility during rou-
side effects include sedation, addiction, and respiratory depres-
tine manipulations. The benzyl group was then removed by
sion.1 Agonists of the delta opioid receptor should lack these side
effects while providing pain relief. Recent evidence also link
agonism of the delta opioid receptor to antidepressant and
anxiolytic effects, and this has been validated in preclinical,
in vivo models.2–7 Compound 1 was identified as an orally avail-
able, high-affinity delta opioid receptor agonist, and to further
probe its biological activity, it was required in labeled form.8
hydrogenation in a Parr shaker at 50 psi to give [ethyl-2H4]-4.
Because this material was not isolated free of solvent, a small-
scale peptide coupling with benzoic acid was performed using
[ethyl-2H4]-4 as the limiting reagent. This demonstrated that
the yield of [ethyl-2H4]-4 was at least 83%. Crude [ethyl-2H4]-4
was then coupled with acid 2 to give [ethyl-2H4]-1 in moderate
chemical yield. A large excess of [ethyl-2H4]-4 was used in the
peptide coupling because acid 2 was in limited supply and
needed efficient utilization.
Results and discussion
Drug metabolism requested stable isotope labeled 1 with a
minimum mass increase of M + 4. A retrosynthetic analysis
showed a disconnect at the amide bond to give acid 2 and N-
methylaminoethanol (Scheme 1). N-Methylaminoethanol could
aIsotope Chemistry, DMPK, AstraZeneca Pharmaceuticals LP, Wilmington, DE
19850, USA
be labeled with at least a mass increase of 4 in several different bCNS-Chemistry, AstraZeneca Pharmaceuticals LP, Wilmington, DE 19850, USA
manners and seemed an easy target for label incorporation. An
alternate disconnect was at the vinyl–quinoline bond. This
scheme intersected with the medicinal chemistry route, but we felt
the preparation of labeled quinolyl boronic acid would require
cNeuroscience-Biology, AstraZeneca Pharmaceuticals LP, Wilmington, DE 19850,
USA
dCNS-Chemistry, AstraZeneca Pharmaceuticals, SE-15185 Södertälje, Sweden
more time to prepare than labeled N-methylaminoethanol. There-
fore, we opted to investigate the amide coupling first.
eKarolinska Institutet, Department of Clinical Neuroscience, Psychiatry Section,
Karolinska University Hospital, SE-17176 Stockholm, Sweden
Acid 2 was prepared using hydrolysis of a related compound,
and the final compound was purified using preparative HPLC
(Scheme 2). While 1 hydrolyzes readily under the same condi-
fCurrent address: Department of Toxicology, Abbott Laboratories, 100 Abbott
Park Dr, R468, Abbott Park, IL 60064, USA
tions, the use of the morpholine adduct eliminated potential
contamination of the final compound with unlabeled 1. We E-mail: chad.elmore@astrazeneca.com.
*Correspondence to: Charles S. Elmore, Pepparedsleden 1, 431 83 Mölndal, Sweden.
J. Label Compd. Radiopharm 2011, 54 847–854
Copyright © 2011 John Wiley & Sons, Ltd.

C. S. Elmore et al.
Scheme 1. Retrosynthetic analysis for the synthesis of 1 in various labeled forms.
1
Upon careful H NMR analysis of the aromatic region of the 2H5, and 1.5% of 2H4 labeled hydroxyquinoline9 and 92% recovery
spectrum, a 20% impurity of ester [ethyl-2H4]-5 was detected (Scheme 4). The conversion of [2H6]-6 to triflate [2H6]-7 was effected
as a by-product of the reaction (Figure 1). The ester was sepa- in 80% yield, and the subsequent Pd-catalyzed boronylation gave
rated from the amide by using reverse phase HPLC. After separa- boronic acid [2H6]-8 in 28% yield.10,11 The subsequent Suzuki cou-
tion, no detectable amount of ester was observed using HPLC or pling proceeded to give [2H6]-9 in 35% yield after purification using
1H NMR, and the compound was stored at room temperature preparative HPLC. This yield was low because of homocoupling
under N2 as the TFA salt. However, after 2 months of storage, of the boronic acid that was also observed in unlabeled prepara-
re-analysis of the compound showed a 35% impurity of the ester. tions. The homocoupling was overcome in the unlabeled prepara-
The compound was again purified using preparative HPLC, and tions by using an excess of boronic acid. Deprotection of the
the compound was stored this time as the free base. Under these tert-butyloxycarbonyl group afforded the penultimate compound
storage conditions, the rearranged product [ethyl-2H4]-5 was [2H6]-10 in good yield and was followed by coupling of the second-
not observed after storage of several months.
ary amine with thiazolecarboxaldehyde to give [quinoline-2H6]-1 in
Although [ethyl-2H4]-1 worked as an internal standard, the 53% yield after preparative HPLC. The isotopic enrichment of the
Drug Metabolism and Pharmacokinetics (DMPK) Department labeled material was 86% M + 6 with 13% and 0.4% of M + 5 and
requested an alternate labeling scheme. Ideally, the isotopically M + 4, respectively.
labeled portion of the molecule would be contained in the major
The C-14 synthesis was accomplished in one step using a C-14
mass spectral fragments during liquid chromatography (LC)/ carbonylation and is similar to a previously reported route to a
mass spectrometry (MS)/MS analysis. This precluded locating related compound.12,13 The requisite iodide was prepared in four
the stable label in the amide side chain, the thiazolemethyl, or steps (Scheme 5). The carbonylation was then effected using
the piperazine ring which left only two remaining locations: the 1.5 equivalents of sodium [14C]formate and a large excess of N-
quinoline or phenyl ring. We opted for the quinoline ring as it methylethanolamine to give the desired amide in approximately
offered an opportunity to incorporate more than four deuterium 70% crude chemical yield (45% radiochemical yield, Scheme 6).
atoms from relatively inexpensive starting materials. Heating The final compound was purified using preparative HPLC to give
hydroxyquinoline and Pd/C in 2H2O under an atmosphere of an isolated yield of 34% (22% radiochemical) with a radiochemi-
2H2 resulted in high deuterium incorporation: 91% 2H6, 7.6% cal purity of 99.1% and a specific activity of 56 mCi/mmol. This
material was stored as the free base, and no rearranged product
was observed over a period of 1 year.
No selective positron emission tomography radioligand for
imaging central delta opioid receptors in vivo has been reported
to date. Given the high selectivity and potency of 1, we had
interest in preparing it labeled with C-11 for evaluation as a can-
didate positron emission tomography radioligand for the delta
opioid receptor. The precursor for C-11 labeling (11) was
prepared in one step by coupling 2-(t-butyldimethylsiloxy)etha-
namine with acid 2, and 11 was methylated with 11CH3I under
alkaline conditions (Scheme 7). Attempts to selectively [11C]
methylate the amide without an O-protecting group failed. Sub-
sequent deprotection of the silyl group was achieved with tetra-
Scheme 2. Synthesis of 2 by hydrolysis.
butyl ammonium fluoride.
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Copyright © 2011 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2011, 54 847–854

C. S. Elmore et al.
HN
D
D
K2CO3, THF
93%
D
D
H2, Pd/C,
EtOH
HO
N
+
HO
NH
D
D
D
D
D
D
OH
83%
Br
D
D
[ethyl-2H4]-3
[ethyl-2H4]-4
O
O
D
D
D D
HO
MeNH
N
O
D
D
D D
2, NMM,
TBTU, DMF
65%
N
N
N
N
N
S
N
S
[ethyl-2H4]-1
[ethyl-2H4]-5
Scheme 3. Synthesis of [ethyl-2H4]-1 from [2H4]-2-bromoethanol.
1H NMR spectra were recorded on Bruker DPX 300, DRX 400,
Avance 500, and DRX 600 spectrometers in dimethyl sulfoxide
(DMSO)-d6, CDCl3, or CD3OD at 30ꢀC and were referenced to
the residual solvent peak. LC/MS analyses were performed on
an HP MSD-1100 using a 4.6 Â 100-mm Luna-C18(2) column,
with a 10%–100% gradient of MeCN-0.1% aqueous formic acid
for 10 min and electrospray ionization. HPLC analyses were per-
formed using a Agilent 1100 series HPLC system using a
4.6 Â 100-mm Phenomenex Luna C18(2) column followed by a
3-min wash with 100% organic mobile phase unless otherwise
specified. Preparative HPLC purifications were performed on a
21.2 Â 250-mm Phenomenex Luna C18(2) column with a flow
rate of 15 mL/min. Silica gel purifications were performed on a
Teledyne ISCO CombiFlash Companion using gradient elution.
Experimental
2-(t-Butyldimethylsiloxy)ethanamine was prepared according to a lit-
erature procedure.14 H14CO2Na was purchased from American Radi-
olabeled Chemicals, Inc. (St. Louis, MO, USA), 2H2O and Br2H2C2H2OH
were purchased from Cambridge Isotopes Laboratories (Andover,
MA, USA), and 2H2 was purchased from GT&S, Inc. (Wilmington, DE,
USA). Morpholino(4-(quinolin-8-yl(1-(thiazol-4-ylmethyl)piperidin-4-
ylidene)methyl)phenyl)methanone was provided by AstraZeneca
CNS-Chemistry (Wilmington, DE, USA). All other reagents were
obtained from Acros (Pitttsburgh, PA, USA), Sigma-Aldrich (St. Louis,
MO, USA), Fisher (Pitttsburgh, PA, USA), and Strem (Newburyport,
MA, USA) and were used without purification. [11C]Methane was pro-
duced at the Karolinska University Hospital Solna with a GE Medical
Systems PETtrace cyclotron (Uppsala, Sweden) using 16 MeV pro-
tons in the 14N(p,a)11C reaction on a mixture of nitrogen and hydro-
gen gas (10% hydrogen). [11C]Methane was isolated from the target
gas on a cooled N2(l) Porapak Q trap and subsequently converted
into [11C]methyl iodide using radical iodination in a recirculation sys-
tem as previously described elsewhere.15
4-(quinolin-8-yl(1-(thiazol-4-ylmethyl)piperidin-4-ylidene)
methyl)benzoic acid (2)
A solution of 917 mg (1.80 mmol) of morpholino(4-(quinolin-8-yl
(1-(thiazol-4-ylmethyl)piperidin-4-ylidene)methyl)phenyl)metha-
none in 30 mL of 6 M HCl was purged with N2 and then stirred
and heated at 120ꢀC overnight in a sealed tube. The solvent
was removed under vacuum, and the residue was dissolved in
100 mL of water. The solution was applied to an Oasis HLB Sep-
Pak, and after washes with saturated NaHCO3 and water, the
compound was eluted with 100 mL of MeCN. The organic solu-
tion was concentrated to dryness, and 100 mL of BuOAc was
added to the resulting tan solid. The slurry was concentrated to
dryness to afford 752 mg of 2 as a tan solid. LC/MS (M + 1): 442
(100%), 443 (30%), 444 (10%). 1H NMR (500 MHz, DMSO-d6) d
ppm 1.95 (m, 2 H), 2.39 (m, 4 H), 2.65 (m, 2 H), 3.69 (s, 2 H),
7.37 (d, J = 8.2 Hz, 2 H), 7.49 (m, 2 H), 7.59 (m, 2 H), 7.81 (d,
J = 8.2 Hz, 2 H), 7.90 (dd, J = 6.0, 3.6 Hz, 1 H), 8.33 (dd, J = 8.2,
1.5 Hz, 1 H), 8.87 (dd, J = 4.0, 1.6 Hz, 1 H), 9.02 (d, J = 1.8 Hz, 1 H).
N-Benzyl-N-methyl-[1,2-2H4]-2-hydroxyethylamine
([ethyl-2H4]-3)
1
Figure 1. Stacked H NMR (DMSO-d6, 90ꢀC) plot of impure (65%) and enriched
(95%) [ethyl-2H4]-1. The ester is best detected at a chemical shift of 7.43 ppm
but can also be seen at 8.87 and 9.15 ppm.
A slurry of 2.12 mL (16.6 mmol) of N-methyl benzylamine, 2.78 g
(21.6 mmol) of [1,2-2H4]-2-bromoethanol, and 6.87 g (49.8 mmol)
J. Label Compd. Radiopharm 2011, 54 847–854
Copyright © 2011 John Wiley & Sons, Ltd.
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C. S. Elmore et al.
Scheme 4. Preparation of [quinoline-2H6]-1 from [2H6]quinoline.
Scheme 5. Preparation of the starting iodide for the C-14 carbonylation.
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Copyright © 2011 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2011, 54 847–854

C. S. Elmore et al.
(0.64 mmol) of O-(Benzotriazol-1-yl)-N,N,N’,N-tetramethyluronium
tetrafluoroborate (TBTU) were added. The solution was stirred
10min at room temperature, and ca. 200 mg (2.7 mmol) of
[ethyl-2H4]-4 was added in 3 mL of DMF. The solution was stirred
for 2 h at room temperature and was then partitioned between
150 mL of ethyl acetate and 100 mL of aqueous 3% citric acid.
The layers were separated, and the aqueous layer was extracted
with 150mL of EtOAc. The combined organic layers were extracted
with 100 mL of saturated aqueous NaHCO3 and 100mL of satu-
rated aqueous NaCl. The organics were concentrated and purified
using silica gel chromatography (MeOH-CH2Cl2) to give 250 mg of
[ethyl-2H4]-1 (80% UV area%, 2%–40% MeCN-0.1% formic acid for
20min). This material was then purified using preparative HPLC
(5%–40% MeOH-0.1% TFA for 40 min followed by 40%–60% for
10min), and the product was isolated by elution of the product
in EtOH from an Oasis HLB SepPak to give 85 mg of [ethyl-2H4]-1
(>99% UV area%, same method). LC/MS: (M+ H): 503 (100), 504
(31.5), 505 (9.9%). 1H NMR (500 MHz, DMSO-d6) d ppm 1.91 (m, 2
H), 2.34 (m, 1 H), 2.41 (d, J = 5.8 Hz, 2 H), 2.64 (m, 1 H), 2.73 (s, 2
H), 2.90 (m, 5 H), 3.67 (s, 2 H), 4.65 (s, 1 H), 7.26 (d, J = 7.3 Hz, 1 H),
7.30 (d, J = 7.6 Hz, 1 H), 7.48 (s, 1 H), 7.49 (dd, J = 7.9, 4.1 Hz, 1 H),
7.58 (s, 1 H), 7.59 (d, J = 2.1Hz, 1 H), 7.89 (dq, J = 6.0, 3.5 Hz, 1 H),
8.33 (dd, J = 8.2, 1.8 Hz, 1 H), 8.89 (dd, J = 4.0, 1.5Hz, 1 H), 9.01 (d,
J = 2.1 Hz, 1 H).
Scheme 6. Preparation of [14C]-1 by C-14 carbonylation.
of potassium carbonate in 20 mL of tetrahydrofuran was stirred
for 72 h. The mixture was filtered, and the filtrate was concen-
trated to dryness. The residue was purified using silica gel chro-
matography (MeOH-CH2Cl2). The pure fractions were combined
and concentrated to give 2.6 g (93%) of [ethyl-2H4]-3 as a clear
oil. LC/MS (M + H): 170 (100%), 171 (12.5%), 168 (1.1%). H NMR
(300 MHz, DMSO-d6) d ppm 2.13 (s, 3 H) 3.48 (s, 2 H) 4.29 (s, 1
H) 7.24 (m, 1 H) 7.30 (m, 4 H)
1
N-methyl-[1,2-2H4]-2-hydroxyethylamine ([ethyl-2H4]-4)
[2H6]quinolin-8-ol ([2H6]-6)
A mixture of 1.3 g (7.2 mmol) of [ethyl-2H4]-3 and 90 mg of 10%
palladium on carbon in 20 mL of ethanol was pressurized to
50 psi with H2 in a Parr shaker and was shaken for 2 h at room
temperature. The mixture was filtered, and the filtrate was con-
centrated to near dryness. The crude residue was taken up in
20 mL of ethanol, and 67 mg of 10% palladium on carbon was
added. The slurry was pressurized to 50 psi with H2 in a Parr sha-
ker and was shaken for 5 h. The mixture was filtered and concen-
trated to near dryness to give 4 as a yellow oil (ca. 600 mg of
pure material). The oil was dissolved in 9 mL of dimethylforma-
mide (DMF) to ease transfer into the next reaction. A probe pep-
tide coupling was used to assess the amount of [ethyl-2H4]-4;
30 mg (0.40 mmol) of [ethyl-2H4]-4 and 50 mg (0.41mmol) of
PhCO2H were reacted as described for [ethyl-2H4]-1 to give
57 mg (78%) after purification using silica gel chromatography.
A pressure vessel was charged with 1.6 g (11 mmol) of quinolin-8-ol,
158 mg of 5% Pd/C, and 76 mL of 99.8% D2O. The vessel was
purged first with N2 and then with H2, and the vessel was then
2
sealed. The reaction mixture was then stirred and heated at 145ꢀC
for 16 h. The reaction was cooled to room temperature and was
diluted with 50 mL of EtOAc. The biphasic mixture was filtered,
and the layers were separated. The aqueous layer was extracted
twice with 50 mL of EtOAc. The combined organic layers were dried
(Na2SO4) and filtered, and the resulting solution was concentrated
to dryness. The residue was taken up in a minimum of EtOAc and
was passed through a plug of silica gel. The solvent was removed
to give 1.56 g of [2H6]-6 as a yellow solid. LC/MS (M + H): 152
(100%), 153 (13.0%), 151 (8.4%), 150 (1.6%).
[2H6]quinolin-8-yl trifluoromethanesulfonate ([2H6]-7)
N-([1,2-2H4]-2-hydroxyethyl)-N-methyl-4-(quinolin-8-yl
(1-(thiazol-4-ylmethyl)piperidin-4-ylidene)methyl)
benzamide ([ethyl-2H4]-1)
A stirred solution of 1.56 g (10.3 mmol) of [2H6]quinolin-8-ol and
2.5 mL (31.0 mmol) of pyridine in 18 mL of CH2Cl2 was cooled in
an ice bath as 2.26 mL (13.4 mmol) of trifluoromethanesulfonic
A solution of 230 mg (0.56 mmol) of 2 in 2 mL of DMF was stirred anhydride in 18 mL of CH2Cl2 was added dropwise. This mixture
as 0.45 mL (4 mmol) of N-methylmorpholine and 210 mg was stirred for 10 min at 0ꢀC and 1 h at room temperature. The
Scheme 7. Preparation of [11C]-1 by 11C-methylation.
J. Label Compd. Radiopharm 2011, 54 847–854
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C. S. Elmore et al.
solution was then cooled to 0ꢀC, and 20 mL of H2O was added. concentrated to dryness to give 82 mg of [2H6]-10 as a white
The layers were separated, and the aqueous layer was extracted foam. HPLC analysis (5%–100% MeCN-0.1% formic acid for
with 50 mL of CH2Cl2. The combined organic extracts were 10 min) showed a purity of 96.3% UV area% purity. LC/MS
washed with 50 mL of 1 M HCl, 50 mL of brine, and 50 mL of water (M + H): 406 (1.3%), 407 (16.8%), 408 (100%), 409 (43.1%). 1H
and were then dried (MgSO4). The drying agent was removed, NMR (500 MHz, CDCl3) d ppm 2.1 (m, 2H), 2.35 (m, 1H), 2.70 (m,
and the resulting solution concentrated to dryness to give an 4 H), 3.0 (m, 3H), 3.2 (m, 2H), 3.8 (m, 4H), 7.31 (m, 4 H). LC/HRMS:
orange solid that was purified using silica gel chromatography expected: 408.25526, found: 408.25513.
to give 2.35 g (8.30 mmol) of [2H6]-7 as a yellow solid. LC/MS
(M + H): 284 (100%), 283 (19.7%), 285 (18.2%), 282 (2.8%).
N-(2-hydroxyethyl)-N-methyl-4-([2H6]quinolin-8-yl
(1-(thiazol-4-ylmethyl)piperidin-4-ylidene)methyl)
[2H6]quinolin-8-ylboronic acid ([2H6]-8)
benzamide ([quinioline-2H6]-1)
A solution of 3.44 g (12.2 mmol) of [2H6]-7, 4.63 g (18.2 mmol) of A solution of 40 mg (0.10 mmol) of [2H6]-10 and 17 mg of
bis(pinacolato)diboron, 337 mg (0.61 mmol) of 1,1′-bis(diphenyl- (0.15 mmol) of thiazole-4-carbaldehyde (16.66 mg, 0.15 mmol)
phosphino)ferrocene (dppf), 496 mg (0.61 mmol) of PdCl2 in 3 mL of methanol was stirred for 3 h and then 18.5 mg
(dppf)-CH2Cl2, and 3.58 g (36.5 mmol) of KOAc in 75 mL of diox- (0.29 mmol) of NaBH3CN was added, and the resulting solution
ane was thoroughly degassed and then stirred at 80ꢀC overnight was stirred for 30 min. The solution was diluted with 5 mL of
under N2. The solvent was removed at reduced pressure to give CH2Cl2 and 5 mL of saturated aqueous NaHCO3, and the layers
a dark brown solid that was dissolved in hot MeOH and filtered were separated. The aqueous layer was then extracted four times
through a celite pad. The solvent was removed, and the residue with 5 mL of CH2Cl2, and the combined organic layers were dried
partitioned between 200 mL of Et2O and 100 mL of 3 N HCl. The (MgSO4) and filtered. The solution was concentrated to dryness
organic layer was extracted with 50 mL of 3 M HCl, and the com- and then purified using preparative HPLC (20%–80% MeOH-
bined aqueous layers were then extracted with 100 mL of Et2O. 0.1% TFA for 20 min). Product containing fractions were
The pH of the aqueous solution was adjusted to 7 using aqueous neutralized with saturated aqueous NaHCO3 as soon as they
NaOH, and the precipitant was isolated using filtration. The pre- were collected and were subsequently combined and extracted
cipitant was washed with EtOAc and was then dried to give four times with 50 mL of CH2Cl2. The combined organic layers
614 mg of [2H6]-8 as an oily orange solid. LC/MS (M + H): 178 were dried (MgSO4) and filtered, and the resulting solution was
(0.9%), 179 (24.7%), 180 (100%), 181 (10.4%).
concentrated to dryness to give 26 mg of a white solid. HPLC
analysis (5%–100% MeCN-0.1% formic acid for 10 min) showed a
purity of >99% UV area%. LC/MS (M+ H): 503 (0.5%), 504
(15.4%), 505 (100%), 506 (36.7%). 1H NMR (500MHz, CDCl3) d
ppm 2.09 (m, 2H), 2.41(m, 1H), 2.59 (m, 4 H), 2.74 (m, 1H), 3.00 (br
s, 3H), 3.66 (br s, 2H), 3.76 (s, 2 H), 3.85 (br s, 2H), 7.18 (s, 1 H),
7.30 (d, J = 6.4Hz, 2 H), 7.34 (d, J = 6.4Hz, 2 H), 8.75 (s, 1 H), 9.01
(s, 0.15 H). LC/HRMS: calculated: 505.25388, found: 505.25299.
t-butyl 4-((4-((2-hydroxyethyl)(methyl)carbamoyl)phenyl)
([2H6]quinolin-8-yl)methylene)piperidine-1-carboxylate
([2H6]-9)
A solution of 586mg (1.29 mmol) of t-butyl 4-(bromo(4-((2-
hydroxyethyl)(methyl)carbamoyl)phenyl)methylene)piperidine-1-
carboxylate and 17 mg (0.078 mmol) of Pd(OAc)2 in 3 mL of MeCN
was heated to 76ꢀC and was then added to a mixture of 255 mg
(1.42 mmol) of [2H6]-8 and 447 mg (3.23 mmol) of K2CO3 in
t-butyl 4-(quinoline-8-carbonyl)piperidine-1-carboxylate
1.25mL of water. The resulting mixture was then stirred overnight A solution of 4.9 g (23 mmol) of 8-bromoquinoline in 83 mL of
at 76ꢀC. The reaction mixture was diluted with 50 mL of brine and THF was cooled at À78ꢀC and stirred as 15 mL (23 mmol) of
was then extracted five times with 50 mL of EtOAc. The combined 1.5 M s-BuLi in cyclohexane was added. The reaction mixture
extracts were dried (MgSO4) and then filtered. The solution was was stirred for 30 min at À78ꢀC and then 5.0 g (18 mmol) of
concentrated to dryness, and the residue was purified using pre- t-butyl 4-(methoxy(methyl)carbamoyl)piperidine-1-carboxylate
parative HPLC (20%–50% MeCN-0.1% TFA for 20 min); the product was slowly added. After 1 h at À78ꢀC and 2 h at room tempera-
containing fractions was pooled and basified with Na2CO3, and the ture, the mixture was diluted with water and extracted twice
MeCN was removed. The suspension was then passed through an with 50 mL of EtOAc. The combined organic layers were washed
Oasis HLB SepPac, and the compound was eluted with MeOH. The with water and saturated aqueous NaCl and then dried (Na2SO4).
MeOH was removed to give 230 mg of [2H6]-9 as an orange oil. The solution was filtered, and the filtrate was concentrated to
LC/MS (M+ H): 506 (2.3%), 507 (25.7%), 508 (100%), 509 (42.0%).
dryness. Purification using silica gel chromatography (hexane-
EtOAc) afforded 3.7 g of t-butyl 4-(quinoline-8-carbonyl)piperi-
dine-1-carboxylate as a viscous oil. 1H NMR (400 MHz, CDCl3)
d ppm 1.46 (s, 9H), 1.65 (m, 2H), 1.94 (m, 2H), 2.87 (m, 2H), 3.88
(m, 1H), 4.11 (m, 2H), 7.47 (m, 1H), 7.59 (m, 1H), 7.78 (m, 1H),
7.93 (m, 1H), 8.21 (m, 1H), 8.95 (m, 1H).
N-(2-hydroxyethyl)-N-methyl-4-(piperidin-4-ylidene([2H6]
quinolin-8-yl)methyl)benzamide ([2H6]-10)
A solution of 130 mg (0.26 mmol) of [2H6]-9 in 1.8 mL of CH2Cl2
and 0.12 mL of MeOH was stirred as 0.64 mL of 4 M HCl in diox-
ane was added dropwise for 5 min. The solution was stirred for
15 min and then basified with aqueous Na2CO3. The reaction
mixture was extracted three times with 10 mL of CH2Cl2, and
t-butyl 4-(hydroxy(4-iodophenyl)(quinolin-8-yl)methyl)
piperidine-1-carboxylate
the combined organic layers were dried (MgSO4). The drying A solution of 1,4-diidobenzene (2.52 g, 7.6 mmol) in 20 mL of THF
agent was removed using filtration, and the solution was con- was stirred at À78ꢀC as 5.0 mL of 1.4 M n-BuLi in hexane was
centrated to dryness. The residue was purified using column added and was stirred for 1 h. A solution of 1.0 g (2.9 mmol) of
chromatography on basic alumina to give 83 mg of a clear oil. t-butyl 4-(quinoline-8-carbonyl)piperidine-1-carboxylate in 6 mL
The oil was taken up in a minimum of MeCN and then of THF was slowly added, and the resulting solution was stirred
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J. Label Compd. Radiopharm 2011, 54 847–854

C. S. Elmore et al.
for 1 h at À78ꢀC and at room temperature for 3 h. The reaction of DMF was cooled to À70ꢀC. The apparatus was evacuated to
mixture was diluted with water and then extracted twice with 1 mbar, and the stopcock to the vacuum was closed. Following
50 mL of EtOAc. The combined organic layers were washed with slow addition of 24 mL of H2SO4 through the septum of the
water and saturated aqueous NaCl and then dried (Na2SO4). The three-necked flask, the mixture was warmed to 110ꢀC and the
solution was filtered, and the filtrate was concentrated to one-necked flask was warmed to 80ꢀC. The contents of both
dryness. The residue was purified using silica gel chromatogra- flasks were stirred vigorously overnight. The reaction mixture
phy (hexane-EtOAc) to give 1.0 g of t-butyl 4-(hydroxy(4- was cooled to room temperature and was diluted with 6 mL of
iodophenyl)(quinolin-8-yl)methyl)piperidine-1-carboxylate as
a
0.1% TFA. The resulting solution was filtered and then purified
white solid. 1H NMR (400 MHz, CDCl3) d ppm 1.44 (s, 9H), 1.65 (m, using preparative HPLC (5%–40% MeOH-0.1% TFA for 40 min fol-
2H), 1.82 (m, 2H), 2.5 (m, 1H), 2.7 (m, 2H), 4.15 (m, 3H), 7.28 (d, lowed by 40%–60% for 10 min). The fractions were analyzed
J = 8.4Hz, 2H), 7.37 (m, 1H), 7.54 (d, J = 8.4 Hz, 2H), 7.61 (m, 1H), using HPLC (10%–30% MeOH-0.1% TFA on 4.6 Â 100-mm
7.75 (m, 1H), 7.83 (m, 2H), 8.16 (m, 1H), 8.71 (m, 1H), 9.65 (s, 1H).
Thermo Scientific Hypersyl Gold column for 20 min), and the
pure fraction were combined and basified with 30 mL of satu-
rated aqueous NaHCO3. The solution was extracted three times
with 50 mL of CH2Cl2, and the combined organic layers were
dried (MgSO4). The drying agent was removed using filtration,
and the solvent was removed to give a 4 mCi of a gummy white
solid. HPLC assay showed a purity of 99.1% (30%–50% MeOH-
0.1% TFA on a 4.6 Â 150-mm Phenomenex RP-Polar column for
20 min followed by wash). LC/MS: 501 (100%), 502 (35.4%), 499
8-((4-iodophenyl)(piperidin-4-ylidene)methyl)quinoline
A solution of 1.0 g (1.8 mmol) of t-butyl 4-(hydroxy(4-iodophenyl)
(quinolin-8-yl)methyl)piperidine-1-carboxylate in 25 mL of PhCH3
and 7 mL of 3 mL H2SO4 was stirred and heated at reflux with
azeotropic collection of water for 4 h. The reaction mixture was
cooled to room temperature and was diluted with 10 mL of
water. The pH of the aqueous phase was adjusted to 10 with
5 M NaOH, and the layers were separated. The aqueous layer
was extracted twice with 25 mL of PhCH3, and the combined
organic layers were washed with water and saturated aqueous
NaCl and were then dried (Na2SO4). The solution was filtered,
and the filtrate was concentrated to dryness. The residue was
purified using silica gel chromatography (MeOH-CH2Cl2) to
afford 0.80 g of 8-((4-iodophenyl)(piperidin-4-ylidene)methyl)
quinoline as a yellow solid. 1H NMR (400 MHz, CDCl3) d ppm
1.93 (m, 2H), 2.51 (m, 2H), 2.78 (m, 1H), 2.94 (m, 2H), 3.09
(m, 1H), 7.08 (m, 2H), 7.37 (m, 1H), 7.51 (m, 2H), 7.55 (m, 2H),
7.74 (m, 1H), 8.13 ( m, 1H), 8.92 (m, 1H).
1
(11.9%). H NMR (500 MHz, DMSO-d6) d ppm 2.35 (m, 5 H), 2.42
(m, 3 H), 2.91 (br s, 6 H), 3.67 (s, 5 H), 4.65 (s, 2 H), 7.25 (m, 4
H), 7.30 (m, 4 H), 7.47 (d, J = 1.8 Hz, 2 H), 7.49 (m, 2 H), 7.58 (s, 2
H), 7.59 (d, J = 2.1 Hz, 2 H), 7.88 (m, 2 H), 8.32 (m, 2 H), 8.89 (m,
2 H), 9.01 (d, J = 2.1 Hz, 2 H).
N-(2-(t-butyldimethylsilyloxy)ethyl)-N-methyl-4-(quinolin-8-
yl(1-(thiazol-4-ylmethyl)piperidin-4-ylidene)methyl)
benzamide, 11
A solution of 120 mg (0.27 mmol) of acid 2, 320 mg (1.0 mmol) of
TBTU, and 0.05 mL (0.36 mmol) of NEt3 in 2 mL of DMF was stir-
red at room temperature as 50 mg (0.28 mmol) of 2-(t-butyldi-
methylsilyloxy)ethanamine was added. After 30 min, the reaction
mixture was diluted with 15 mL of water, and the resulting emul-
sion was extracted four times with 5 mL of CH2Cl2. The combined
organic layers were dried (MgSO4) and filtered, and the resulting
filtrate was concentrated to dryness. The residue was purified
using three iterative RP-HPLC purifications (30 Â 100-mm Gemini
C18, 2%–95% MeCN-NH4HCO3 (pH 10) for 20 min) to give 38 mg
of 11. LC/MS (M + H): 599 (100%), 600 (52%), 601 (18%). 1H NMR
(500 MHz, DMSO-d6) d ppm 0.00 (s, 9 H), 0.83 (s, 6 H), 1.94 (m, 2
H), 2.38 (m, 4 H), 2.63 (m, 2 H), 3.30 (m, 2 H), 3.63 (t, J = 6.4 Hz,
2 H), 3.67 (s, 2 H), 7.32 (d, J = 8.2 Hz, 2 H), 7.48 (m, 2 H), 7.59 (m,
2 H), 7.67 (d, J = 8.5 Hz, 2 H), 7.89 (m, 1 H), 8.28 (t, J = 5.8 Hz, 1
H), 8.32 (dd, J = 8.4, 1.7 Hz, 1 H), 8.87 (dd, J = 4.1, 1.7 Hz, 1 H),
9.01 (d, J = 2.1 Hz, 1 H).
4-((4-((4-iodophenyl)(quinolin-8-yl)methylene)piperidin-
1-yl)methyl)thiazole
A solution of 500 mg (1.17 mmol) of 8-((4-iodophenyl)(piperidin-4-
ylidene)methyl)quinoline and 219 mg (1.94 mmol) of thiazole-4-
carboxaldehyde (219 mg, 1.94 mmol) in 20 mL of 1,2-dichloroethane
was stirred as 510 mg (2.4 mmol) of NaB(OAc)3H was added, and the
resulting solution was stirred at room temperature for 2 h. The reac-
tion mixture was diluted with 1 N NaOH and was extracted twice
with 20 mL of CH2Cl2. The combined organic layer was dried
(Na2SO4) and filtered, and the filtrate was concentrated to dryness.
The residue was purified using silica gel chromatography (MeOH-
CH2Cl2) to give 350 mg of 4-((4-((4-iodophenyl)(quinolin-8-yl)methy-
lene)piperidin-1-yl)methyl)thiazole as a greenish-yellow solid. 1H
NMR (400 MHz, CDCl3) d ppm 2.08 (m, 2H), 2.43 (m, 1H), 2.64 (m,
4H), 2.78 (m, 1H), 3.80 (s, 2H), 7.06 (d, J= 8 Hz, 2H), 7.25 (m, 1H),
7.36 (m, 1H), 7.49 (m, 2H), 7.54 (d, J= 8 Hz, 2H), 7.73 (m, 1H), 8.12
(m, 1H), 8.77 (s, 1H), 8.90 (m, 1H).
N-(2-hydroxyethyl)-N-[11C]methyl-4-(quinolin-8-yl(1-(thiazol-
4-ylmethyl)piperidin-4-ylidene)methyl)benzamide ([11C]-1)
[11C]Methyl iodide (5.8 mAh irradiation (35 mA for 10 min)) was
trapped in a solution of 0.5 mg (0.8 mmol) of 11 and 5 mg
(89 mmol) of potassium hydroxide in 350 mL of DMSO. After
entrapment was completed, the reaction mixture was heated
N-(2-hydroxyethyl)-N-methyl-4-(quinolin-8-yl(1-(thiazol-
4-ylmethyl)piperidin-4-ylidene)methyl)benz-[14C]-amide
([14C]-1)
A 50-mL, three-necked flask containing 23 mg (0.33 mmol, at 135ꢀC for 2 min and then 100 mL of 1 M Tetrabutylammonium
18 mCi) of NaO124CH was fitted with a vacuum adapter with a fluoride in THF was added. After heating the resulting mixture for
stopcock, a 90ꢀ bent adapter attached to a 25-mL round bot- 2 min, it was diluted with water and purified using semiprepara-
tomed flask and a septum.12 A one-necked flask containing tive HPLC (300 Â 7.8-mm Waters m-Bondapak C-18 column, 14%
109 mg (0.21 mmol) of 4-((4-((4-iodophenyl)(quinolin-8-yl)methy- MeCN-10 mM H3PO4). The fraction containing [11C]AZD7268 was
lene)piperidin-1-yl)methyl)thiazole, 26 mg (0.036 mmol) of Pd collected, evaporated to dryness, and redissolved in sterile
(dppf)Cl2, 0.2 mL (2 mmol) of 2-(methylamino)ethanol, and 8 mL physiological buffered saline (phosphate buffered saline, pH
J. Label Compd. Radiopharm 2011, 54 847–854
Copyright © 2011 John Wiley & Sons, Ltd.
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C. S. Elmore et al.
7.4) to give 26 mCi of [11C]AZD7268 with a radiochemical purity
of >99% (300 Â 3.9-mm Waters m-Bondapak C-18 column, 15%
MeCN-10 mM H3PO4) and a specific radioactivity of 12,500 Ci/mmol
(determined using HPLC with 300 Â 3.9-mm Waters m-Bondapak
C-18 column, 15% MeCN-50 mM H3PO4).
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Copyright © 2011 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2011, 54 847–854